The invention relates to a mould for tire treads, these treads possibly being intended equally well for capping new tires or for recapping.
In what follows, “inner” surface of a tread will be understood to mean the surface of the tread which is intended to be laid on the tire and therefore oriented towards the inside relative to the center of the tire, and “outer” surface will be understood to mean the surface intended to be in contact with the ground when the tread is laid on the tire and therefore oriented towards the outside relative to the center of the tire.
The invention relates more particularly to an apparatus using a flat mould comprising a first, lower, molding part and a second, upper, molding part each defining respectively the outer surface or the inner surface of the tread, at least one of these molding parts being movable between two positions corresponding to the opening and the closing of the mould.
Nowadays, the person skilled in the art has well mastered the mechanics and kinematics of opening and closing moulds which make it possible correctly to mould and vulcanize a tread. However, at present it is not known how to demold the tread over its entire length simultaneously, but only gradually. Thus the operation of demolding the tread remains tricky, or even is becoming trickier and trickier owing to the increasing complexity of the tread patterns produced on the treads.
In fact, on opening the mould, the tread remains in the lower molding part, which is generally the part defining the molding of its outer surface, and for effecting demolding, one great difficulty which is encountered is producing a “starting point” for detaching the tread, that is to say demolding one of the ends in the longitudinal direction of the tread. What is tricky about this operation is that it has to effect complete demolding of the end without producing defects due, for example, to tearing at the level of a tread pattern and with a minimum of stresses on the tread in order to avoid deformation of the latter.
Furthermore, nowadays frequently flat presses are used which alternately superpose lower and upper plates in order to have several moulds for the same amount of floor space but which of necessity offer a very limited mould-opening space. It is therefore desired that the demolding operation be capable of being effected in a very small space.
Various solutions have been proposed to try to resolve these difficulties. Thus, for example, publication JP 5-111921 describes a tread mould comprising two molding parts in which the part molding the outer surface of the tread bears at one of its longitudinal ends an inclined section intended to form a protuberance relative to the tread on emerging from vulcanization. This protuberance is intended to facilitate the “hooking” of the end in order to effect the demolding. Nevertheless, given its direction parallel to the mould and the thinness thereof, engaging this protuberance appears tricky, and in particular if the tractive effort necessary for demolding the tread has to be great, for example for treads for heavy vehicles.
The invention aims to overcome all these disadvantages.